1. Field of the Invention
The present invention is directed to an implantable medical device of the type having a welded capsule housing which is filled with a gas mixture, and to a method for manufacturing such a device.
2. Description of the Prior Art
In known heart pacemakers, the pacemaker electronics is arranged in a hermetically closed capsule housing, which is filled with a gas mixture of helium and argon. As disclosed, for example, in U.S. Pat. No. 4,174,424, helium is especially well suited for detecting leaks in the capsule housing, due to its extremely small molecules. Argon, by contrast, is preferably employed as a protective gas when welding the capsule housing, as disclosed in U.S. Pat. No. 4,041,956. The known helium-argon gas mixture, however, has relatively poor electrical insulating properties.
A method for manufacturing a film capacitor having a capsule housing filled with an insulating gas such as sulfur hexafluoride, nitrogen or carbon dioxide is disclosed in Japanese Application 55 099 713. A capsule housing for ultra-high frequency circuits whose parts are welded together in a helium-nitrogen atmosphere is disclosed in French Patent 2 648 275. Neither of these publications, however, is directed to an solving the aforementioned problems in the context of an implantable medical device.